Red Dead Redemption 2 has a level of detail that surpasses any other game I can think of. The birds alone are hyper realistic for no clear reason.

If you disturb birds they will fly away and if you follow and watch them they form flocks the same way/shape the exact species does IRL.

Plus many of the other mechanics in the game like the horse physics are unnecessarily realistic IMO, but hot damn if it isn't incredible.